Of Ammianus Marcellinus, the writer of the following History, we know very little more than what can be collected from that portion of it which remains to us. From that source we learn that he was a native of Antioch, and a soldier; being one of the prefectures domestici — the body-guard of the emperor, into which none but men of noble birth were admitted. He was on the staff of Ursicinus, whom he attended in several of his expeditions; and he bore a share in the campaigns which Julian made against the Persians. After that time he never mentions himself, and we are ignorant when he quitted the service and retired to Rome, in which city he composed his History. We know not when he was born, or when he died, except that from one or two incidental passages in his work it is plain that he lived nearly to the end of the fourth century: and it is even uncertain whether he was a Christian or a Pagan; though the general belief is, that he adhered to the religion of the ancient Romans, without, however, permitting it to lead him even to speak disrespectfully of Christians or Christianity.

His History, which he divided into thirty-one books (of which the first thirteen are lost, while the text of those which remain is in some places imperfect), began with the accession of Nerva, A.D. 96, where Tacitus and Suetonius end, and was continued to the death of Valens, A.D. 378, a period of 282 years. And there is probably no work as to the intrinsic value of which there is so little difference of opinion. Gibbon bears repeated testimony to his accuracy, fidelity, and impartiality, and quotes him extensively. In losing his aid after AD. 378, he says, "It is not without sincere regret that I must now take leave of an accurate and faithful guide, who has composed the history of his own times without indulging the prejudices and passions which usually affect the mind of a contemporary." Professor Ramsay (in Smith's Dictionary of Greek and Roman Biography) says, "We are indebted to him for a knowledge of many important facts not elsewhere recorded, and for much valuable insight into the modes of thought and the general tone of public feeling prevalent in his day. Nearly all the statements admitted appear to be founded upon his own observations, or upon the information derived from trustworthy eye-witnesses. A considerable number of dissertations and digressions are introduced, many of them highly interesting and valuable. Such are his notices of the institutions and manners of the Saracens (xiv. 4), of the Scythians and Sarmatians (xvii. 12), of the Huns and Alani (xxxi. 2), of the Egyptians and their country (xxii. 6, 14-16), and his geographical discussions upon Gaul (xv. 9), the Pontus (xxii. 8), and Thrace (xxvii. 4). Less legitimate and less judicious are his geological speculations upon earthquakes (xvii. 7), his astronomical inquiries into eclipses (xx. 3), comets (xxv. 10), and the regulation of the calendar (xxvi. 1); his medical researches into the origin of epidemics (xix. 4); his zoological theory on the destruction of lions by mosquitos (xviii. 7), and his horticultural essay on the impregnation of palms (xxiv. 3). In addition to industry in research and honesty of purpose, he was gifted with a large measure of strong common sense, which enabled him in many points to rise superior to the prejudices of his day, and with a clear-sighted independence spirit which prevented him from being dazzled or overawed by the brilliancy and the terrors which enveloped the imperial throne. But although sufficiently acute in detecting and exposing the follies of others, and especially in ridiculing the absurdities of popular superstition, Ammianus did not entirely escape the contagion. The general and deep-seated belief in magic spells, omens, prodigies, and oracles, which appears to have gained additional strength upon the first introduction of Christianity, evidently exercised no small influence over his mind. The old legends and doctrines of the pagan creed, and the subtle mysticism which philosophers pretended to discover lurking below, when mixed up with the pure and simple but startling tenets of the new faith, formed a confused mass which few intellects could reduce to order and harmony."

The vices of our author's style, and his ambitious affectation of ornament, are condemned by most critics; but some of the points which strike a modern reader as defects evidently arise from the alteration which the Latin language had already undergone since the days of Livy. His great value, however, consists in the facts he has made known to us, and is quite independent of the style or language in which he has conveyed that knowledge, of which without him we should have been nearly destitute.

The present translation has been made from Wagner and Erfurdt's edition, published at Leipzig in 1808, and their division of chapters into short paragraphs has been followed.